(CNN) -- They were crowded into a small rubber boat and pushed out to sea. Like so many other similar journeys, not everyone made it.

Showing signs of physical and mental trauma, 167 migrants, most from sub-Saharan Africa, were rescued off the northwest coast of Libya on Tuesday.

Another 13 -- including two pregnant women and a couple whose four children survived -- perished just 24 hours after setting off on a boat bound for Europe.

Early on in the rescue operation when Spanish NGO Proactiva Open Arms started to move the migrants out of the boat and into the safety of the rescue craft, they found bodies strewn across the bottom of the vessel.

"We are here to rescue people... and when you realize people died, you are there, you know their real situation, you feel the strong reality of the situation," Proactiva Open Arms mission leader Riccardo Gatti told CNN.